import java.util.Scanner;

public class test21 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 递归
        int n = in.nextInt();
        System.out.println(getResult(n));
    }
    public static int getResult(int target){
        if(target==0)
            return 1;
        if (target<0)
            return 0;
        return getResult(target-1)+getResult(target-2);
    }
}
